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Instruments and cigarette lighter light not working
Last time a drove at night I noticed that I have no instruments cluster lights (and the rest of the dash lights), which were working fine until that day.
Warning lights do work as well as headlights and blinkers.
I check the fuses (mainly #38, but also verified other fuses that sounded related) and they are fine.
Car is an 86 944 Turbo
Looking for advice on how to troubleshoot this thing.
A while back, a friend had a random issue with loss of power to all instrument gauges, the cigarette lighter, and the sunroof. This usually occurred after the car had sat for several weeks, and resolved itself each time after driving the car for 5-10 minutes.
Yes, a strange failure mode. I remembered hearing an issue similar to this one, and thought the solution [at that time] was cleaning the contacts of, and/or replacing, the terminal 15 relay. If not mistaken, that relay provides power to a number of circuits. My suggestion...clean the contacts of your term 15 relay and/or replace it with another one.
If you are lucky, maybe Marc [aka marc abrams], our forum electrical subsystem subject matter expert, will chime in and confirm my suspicions.
Though, now that I think about it, the aforementioned issue may have been traced back to the X terminal relay. My revised suggestion...clean the contacts of both the X term and term 15 relays.
The rheostat for the instrument cluster lights and license plate lights both get there power from the #58 buss. Turn on the headlights and check to see if the license plate lights are getting power. This will rule out the headlight switch and everything before it and up to the#38 fuse. Notice I said check for power and not if the license plate lights work. Bad bulbs can throw off the Diagnostics. Marc.
If you are lucky, maybe Marc [aka marc abrams], our forum electrical subsystem subject matter expert, will chime in and confirm my suspicions.
Thanks for the compliment. I owe my electrical skill to the Mack Truck Corporation. Too many years of working on trucks with a 4 inch diameter wire harness going up to the dash, 80+ relays, 6 onboard computers, and 125 page wiring diagrams, these cars are like troubleshooting a flashlight.
I tried to take our several relays including #15 and X. I cleaned the connections (although there was no rust) and put it back in (I do not know how to test them) - didn't help.
I double checked fuse #38 with the test light and it shown green.
I turned on the head lights and the license plate lights came on.
A few weeks ago, I had a stereo guy hook up a dashcam and he tapped into some wires so this may be related (although I had the lights working after he was done).
Here is a photo of how he hooked the wires
this is to the left of the drive left knee under the dash
Okay, set the dimmer to the highest illumination and check the dimmer rheostat for power at both terminals #1 and #2. If you don't have power, it's the wiring between the dimmer and license plate light/dimmer spice. If you have power at terminal#2 but not at #1, it's ether a bad dimmer rheostat or a short down the line. At this point jump the #1 and #2 terminals together. If the dash lights come on, it's a bad dimmer rheostat. If the fuse pops, you have a short. Just make sure that the #38 fuse is the correct 7.5 amp one before you start jumping anything. If it's a short I would start with the radio installation first. Marc.
Okay, set the dimmer to the highest illumination and check the dimmer rheostat for power at both terminals #1 and #2. If you don't have power, it's the wiring between the dimmer and license plate light/dimmer spice. If you have power at terminal#2 but not at #1, it's ether a bad dimmer rheostat or a short down the line. At this point jump the #1 and #2 terminals together. If the dash lights come on, it's a bad dimmer rheostat. If the fuse pops, you have a short. Just make sure that the #38 fuse is the correct 7.5 amp one before you start jumping anything. If it's a short I would start with the radio installation first. Marc.
Thank you so much.
Based on your instructions I am able to nail it down to the dimmer rheostat.
Such a relief...
As an aside, were you able to confirm my suspicions...doesn't the X terminal relay provide 12v to several circuits, including the cluster, cigarette lighter and [possibly] the sunroof?
As an aside, were you able to confirm my suspicions...doesn't the X terminal relay provide 12v to several circuits, including the cluster, cigarette lighter and [possibly] the sunroof?
Thank you. Allen, I'm not aware of a relay for the "X" line. The only "X" output terminal I know of is the output terminal on the ignition switch for the "X" buss line. This is an input to the headlight switch, wipers, and HVAC. The headlight switch has two inputs, the "X" for the headlights and pop up headlight motor signal outputs and the "30" unswitch power for the parking, license plate, and dash light rheostat outputs. The "X" buss does not supply power to sunroof, only the "15" and "30" buss.
Interesting enough, the later cars are wired similar to the early cars. They just have more electrical options so its spread out on to more pages making it more complicated. So late model cars guys, if you are trying to read the later wiring diagrams and your head is spinning, try the early diagrams. Marc.
Last edited by marc abrams; 01-22-2017 at 10:22 AM.
01-12-2017, 07:31 AM
Instruments and cigarette lighter light not working
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